Traffic signals have long been used to regulate the flow of traffic at intersections. Generally, traffic signals have relied on timers or vehicle sensors to determine when to change traffic signal lights, thereby signaling alternating directions of traffic to stop, and others to proceed.
In many installations, the vehicle sensors include inductive loops embedded in the road. An intersection may have loops for each lane of traffic. The loops may also be used for data collection, such as counting the number of vehicles passing through an intersection. The gathered data may be used for improving signal timing and planning road improvements.
Two parameters that are of particular interest in traffic control and road planning are vehicle class and speed. The vehicle class typically refers to the type of vehicle, such as an automobile, pickup, van, vehicle with a trailer, box truck with 2 axles, box truck with more than 2 axles, bus, and tractor trailer. The sizes of vehicles and their speeds can significantly affect the decisions made for improving traffic flow.
Past approaches for collecting vehicle data have been limited to dual loop systems or have provided inaccurate results. One approach relies on two inductive loops embedded in a lane of a road. The space separating the loops and the times at which a vehicle is detected at each loop are used to calculate the vehicle's speed and length. The length may then be used to classify the vehicle. The dual loop approach is limited by the number of roads having embedded dual loops since there may be many road locations at which collection of traffic data is desired, but those locations have only a single loop embedded in the road.
Though some approaches use a single loop to estimate the speed of a vehicle, the results may be inaccurate. When using a single loop to collect vehicle data, it is common to assume that all vehicles have the same length. The speed may be estimated based on the assumed length and the amount of time the vehicle is over the loop. However, the speed may be inaccurate since there may be a large variance between the actual length of the vehicle and the assumed length.